ESR 16:55-63 (2012)  -  DOI: https://doi.org/10.3354/esr00396

ABSTRACT: Seismic airgun arrays are among the most powerful sound sources used at sea, and they have the potential to disrupt the behavior of marine life. Little information is available on marine turtle responses to airgun sounds, and few regulations mandate specific actions to protect turtles from potential impacts of airgun exploration. As part of the French-Algerian project SPIRAL (Sismique Profonde et Investigation Régionale du Nord de l’Algérie) in September and October 2009, visual observations of 164 loggerhead turtles Caretta caretta were conducted during a seismic survey in the Mediterranean Sea off Algeria. The turtles were part of a large aggregation, basking at the surface in calm seas. All sightings occurred during airgun operations, in which shots were fired every 19.4 s (array source level 252 dB re 1 µPa [peak]). Recordings from 3 hydrophones allowed estimation of near-surface airgun sound levels. Of 86 turtles visually tracked until their passage >100 m behind the array, 49 (57%) dove at or before their closest point of approach to the airguns. At least 6 dove immediately following an airgun shot, often showing a startle response. Binomial regression indicated that turtle dive probability decreased with increasing distance from the airgun array. The observed diving behavior may be interpreted as an avoidance response to airguns.

KEY WORDS: Loggerhead · Sea turtle · Caretta caretta · Airgun · Seismic · Noise · Dive behavior